U.S. Pat. No. 4,620,925 issued 4 Nov. 1986, which is assigned to the assignee of this application, discloses an earlier version of an aerating unit for incorporation in an aerobic sewage treatment system. U.S. Pat. No. 5,451,316 issued 19 Sep. 1995, also assigned to the assignee of this application, discloses a later invented combination of the aerating unit into a single tank aerobic system in which one or more directed streams from the aerating unit are arranged to achieve a desired flow of aerated effluent returning from a settling chamber into the aerobic treatment chamber.